1. Field of the Invention
The present invention relates to a combustor of a gas turbine engine including a fuel injection structure of a composite combustion type comprising a combination of two combustion systems, i.e., a diffusion combustion system and a lean pre-mixture combustion system.
2. Description of the Related Art
For the gas turbine engine, in view of the environmental protection, strict criteria are provided, with respect to the composition of exhaust gases to be generated by combustion. In the criteria, reduction of harmful matters, such as nitrogen oxides (hereinafter, referred to as NOx), is greatly required. On the other hand, in the case of large-size gas turbines and/or engines for airplanes, from the requirements of reducing the fuel consumption and enhancing the output, the pressure ratio currently tends to be set higher. With such a tendency, higher temperature and/or higher pressure operation is to be employed around the inlet of the combustor. Therefore, due to such operations to elevate the temperature and/or pressure around the inlet of the combustor, the combustion temperature may also tend to be higher, leading to further increase of NOx.
In recent years, a composite combustion method has been proposed, in which the lean pre-mixture combustion system that can effectively reduce an amount of generation of NOx and the diffusion combustion system excellent in both of the ignition performance and the flame holding performance are combined together. In the lean pre-mixture combustion system, air and a fuel are mixed in advance so as to combust or burn the so-obtained mixed gas or mixture, with the fuel concentration of the gas being kept uniform. Thus, there should be no region in which the flame temperature is locally elevated. In addition, the flame temperature can be lowered over the whole region due to such dilution of the fuel. Therefore, the amount of generation of NOx can be effectively reduced. However, because a considerably great amount of air is to be mixed uniformly with the fuel, a local fuel concentration in the combustion region may tend to be significantly low. In particular, the stability of combustion, especially upon lower intensity combustion, is likely to be deteriorated. On the other hand, the diffusion combustion system is configured to perform combustion while diffusing and mixing the fuel and air. Therefore, flame failure of the combustion is not likely to occur even upon the lower intensity combustion, presenting a superior flame holding performance. Accordingly, the composite combustion system as described above can ensure the stability of combustion, due to a diffusion combustion region to be formed upon starting the operation and/or upon the lower intensity combustion, as well as can reduce the amount of generation of the NOx, due to a lean pre-mixture combustion region to be formed upon higher intensity combustion.
A combustor based on the composite combustion system includes a fuel spray part configured to spray a fuel, so as to form the diffusion combustion region in a combustion chamber, due to the diffusion combustion system, and a pre-mixture supply part configured to supply a pre-mixture of the fuel and air, so as to form the pre-mixture combustion region in the combustion chamber, due to the lean pre-mixture combustion system. The combustor is configured to supply the fuel only from the fuel spray part upon starting the operation and/or upon a lower intensity combustion mode, while, on a higher intensity combustion mode, it is configured to supply the fuel also from the pre-mixture supply part. In this case, during the transition from the lower intensity combustion mode to the higher intensity combustion mode, the distribution ratio of the fuel to the fuel spray part and to the pre-mixture supply part should be controlled, for example, from 1:0 to 1:9, while keeping appropriate conditions for the combustion stability and reduction of NOx.
Conventionally, in order to achieve such a complicated control, flow control valves have been provided to a pilot fuel passage for supplying the fuel to the fuel splay part as well as to a main fuel passage for supplying the fuel to the pre-mixture supplying part, respectively, wherein the flow control valves are controlled by a controller, respectively (JP 5-52124 A).